Within a petroleum producing well, the production string forms the primary conduit through which production fluids (liquids, gases, or any fluid produced from a wellbore) are produced to the surface. The production string is typically assembled with production tubing and completion components in a configuration that suits the wellbore conditions and the production method. Oil wells typically vary from a few hundred to several thousand feet in depth, and there is often insufficient formation pressure to cause the flow of production fluids through the production string to the surface.
Several prior art systems involving different pumping and extraction devices have been developed for the surface transfer of production fluids from a well. Downhole hydraulic pumps installed deep within the well are commonly used. A surface hydraulic pump pressurizes power oil which drives the downhole pump. When a single production string is used, the power oil is pumped down the tubing and a mixture of the formation crude oil and power oil are produced through the casing-tubing annulus. If two production strings are used, the power oil is pumped through one of the pipes, and the mixture of formation crude oil and power oil are produced in the other, parallel pipe.
Prior art artificial lift systems include for example, the progressive cavity pump and plunger lift, both of which are installed on jointed or continuous rods; electric submersible pumps; gear pumps installable on tubing and powered by downhole electric or hydraulic motors; and the venturi lift which is run on coiled tubing but is not a total production system. However, such systems tend to be complex and/or of substantial size and weight, requiring significant structural support elements at the wellhead which increase the expense of the overall system.